The hip joints of today's popular bipedal robots have many
limitations. More articulation in this area would allow much
greater range of motions.

After playing around a bit, I have come up with a design
which I intend to use in my RoboDo project. Here's a rough
picture...

The "stride" servos (the topmost ones) are connected to
their respective legs with either chain or gears, which
allows us to reduce the 180 degree servo motion to 120
degrees. This will produce a modest gain in power while
limiting the travel in this joint to 75 degrees forward and
45 degrees backwards.

The main benefit however, is that this allows us to have the
leg joint supported by a solid shaft and 2 bearings.

The leg rotate servos are also supported by 2 bearings. I
just don't like the idea of hanging the whole leg off of a
single, cantilevered support point.

At first glance, the "leg lift" servos (the lowest ones
pictured) may seem redundant, but these servos will allow
RoboDo to kick higher when the legs are rotated to their
normal walking position, and allow freedom of motion in this
area when the legs are rotated to other positions.